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Proxies

  • often used by hackers to conceal their identity and obfuscate their location
    • these special intermediary servers boast many important real-life applications
      • within the context of caching, access control, censorship bypassing, amongst other things
  • there are 2 primary types of proxies
    • Forward Proxy also normally referred to as just Proxy, Reverse Proxy

Terms used​

Forward Proxy​

  • a server that sits between clients and servers and acts on behalf of the client,
    • typically used to mask the client's identity (IP address)
      • server would normally only be able to see the proxy IP address and not the client
      • do note that there are some proxies that might still make the source IP address retrievable or visible in some way to the server
    • note that forward proxies are often referred to as just proxies
  • the client does a request that's meant to go to the server, but first goes to the forward proxy
    • forward proxy will then forward the request to the server
    • then the server gets the request from the proxy and not from the client
    • when the server responds, it will give its response to the proxy
    • the proxy will then return the response to the client
  • this is a simple example of how VPNs work, allowing you to access websites not accessable from your home country
  • key point is the server thinks it is interacting with the client directly

Reverse Proxy​

  • a server that sits between clients and servers and acts on behalf of the servers
    • typically used for logging, load balancing, or caching
    • when the client makes a DNS query, it will only see the reverse proxy IP address
  • when the client sends a request to the server, it thinks it is sending to the server directly
    • however, it is actually being sent to the reverse proxy configured by the server side first
    • the reverse proxy will then forward the request to the server
    • then the server will return a response back to the reverse proxy
    • the reverse proxy will then return back the response to the client
  • this is a good tool to have in a system design
    • can be used to filter out requests to ignore
    • or can be used to take care of logging for the system
    • 1 of the best use case is to use the reverse proxy as a load balancer
    • also can be used for security purposes
      • if there is a malicious client that wishes to bring down the server by issuing a ton of requests to a given server
        • the reverse proxy can act as a shield for that
          • because it will distribute the request as a load balancer evenly amongst the various servers, so that no single server gets all of the requests
  • key point is the client thinks it is interacting with the server directly

Nginx​

  • a popular webserver that is often used as a reverse proxy and load balancer

Load Balancer​

  • it is something like a server that is gonna effectively distribute or that can distribute load, like request load between a bunch of servers
  • when designing a complex system, there will be a bunch of servers
    • then we can use the reverse proxy to work as a load balancer
      • that decides which incoming requests from clients should be made to which server